LoongArch: KVM: Implement misc vcpu related interfaces

LoongArch: KVM: Implement misc vcpu related interfaces

1, Implement LoongArch vcpu status description such as idle exits
counter, signal exits counter, cpucfg exits counter, etc.

2, Implement some misc vcpu relaterd interfaces, such as vcpu runnable,
vcpu should kick, vcpu dump regs, etc.

Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>